1. Field of the Invention
The present invention relates to a method for producing a light-emitting diode to be used for a display device, a transmission device, and the like.
2. Description of the Related Art
In recent years, light-emitting diodes (LEDs) are widely used in optical communications, information display panels, and the like. In a conventional process for forming an LED into chips, dicing is routinely used. However, after a dicing process, strain typically remains on a diced surface of a substrate. If the chip thus formed is molded with resin without eliminating such strain, luminance is reduced during an operation thereof due to the strain. In an extreme case, simply molding the chip with resin may cause visible dark lines or cracks to be formed.
In order to avoid this problem, the following process is conventionally employed: the strained portion of the chip is removed by etching away the diced surface by several micrometers after the substrate is diced, and then the chip is molded with resin.
For example, in the case of a conventional GaP type LED, after dicing a substrate, the diced surface is etched away by about 3 .mu.m with an etchant of sulfuric acid/hydrogen peroxide type. In the case of a conventional AlGaInP type LED in which Al.sub.x Ga.sub.1-x As (0.ltoreq.x.ltoreq.1) is used to form a current diffusing layer, a diced surface is etched away by 2 .mu.m with a mixture of bromine and methanol.
However, in the case of an AlGaInP type LED using an AlGaAs current diffusion layer, when a light emitting wavelength is shortened (e.g., to the range of 550 to 590 nm), light is likely to be absorbed by the current diffusion layer, thereby reducing luminance. In order to reduce such light absorption, a mole fraction of Al in a mixed crystal in the current diffusion layer may be increased. However, under the conditions of high temperature and high humidity, increased Al mole fraction typically deteriorates the reliability of such an LED.
In order to overcome the above problem, GaP which contains no Al and has a larger energy band gap as compared with AlGaAs may be used to form a current diffusion layer. However, GaP has a lattice mismatch of about 3.6% with respect to a GaAs substrate. Thus, when GaP is used for forming the current diffusion layer to be deposited over a GaAs substrate, strain is likely to be generated, after the dicing process, from a diced surface to a deeper portion of an interface between an AlGaInP light-emitting layer (active layer) and the GaP current diffusion layer. As a result, the AlGaInP light-emitting layer (active layer) and the GaP current diffusion layer is required to be etched away to a deeper position from the diced surface in order to prevent a decrease in luminance.